In a steam turbine, material degradation due to high-temperature heat degradation of a member caused by operating temperature, creep and thermal fatigue degradation, and material degradation resulting from corrosion damage to constructional members of the turbine caused by steam quality have become critical factors governing the life of the steam turbine.
For the former case, it springs from material degradation of the member per se, and therefore it can non-destructively inspect and measure changes in hardness and precipitates of member materials, for understanding of the changes, during routine inspection, and compare the inspected and measured results with a previously acquired deterioration base curve of measurement parameters, thus estimating the residual life of the member.
For the latter case where corrosion is taking part in the material degradation, however, it tends to be become more complex, because of convolution of various factors, differing from relatively stable factors suited for a turbine operation as in the former case, such as temperature, stress, and time. More precisely, the various factors include a change in steam water quality in operation, corrosion resistance of each member, and a difference in environmental conditions varying every vapor flows, temperature distribution in the turbine, surfaces to be exposed to steam, a clearance gap, a degree of condensation in suspension, and a contact part of dissimilar materials. Frequency in operation and suspension, frequency in condensation, and frequency in turbine opening are also important factors. Particularly where a turbine works using geothermal steam, the turbine suffers from large water quality variations, every field of respective plants, and comes to be further added an effect factor to materials by hydrogen sulfide. Corrosion damage due to steam water quality to a member installed in the turbine is a dominant factor governing the life of the geothermal steam turbine.
As a device for detecting such steam water quality, there has been conventionally proposed a steam purity monitoring system, comprising a steam drain device for cooling geothermal steam, and for condensing and liquefying water vapor contained in the geothermal steam; an anion exchange resin for carrying out anion exchange reaction with ingredients contained in the liquefied steam drain; and an electric conductivity measuring means for measuring electric conductivity of the steam drain after the anion exchange reaction, wherein the electric conductivity is measured and monitored as an index indicative of ingredients of the dissolved solids contained in the geothermal steam (e.g. see JP 2002-131261 A).
Also, there has been proposed a corrosive environment damage diagnosis method of mechanical structural parts and a device therefore, comprising detecting and monitoring, at all times, accelerated corrosion parameters of mechanical structural parts materials placed in a corrosive environment, and a corrosive resistance parameter of mechanical structural parts materials; determining whether the corrosive environment inflict damage on the mechanical structural parts materials based on the detected results of the corrosion accelerated parameters; calculating corrosion damage resistance properties based on the detected results of the corrosion resistance parameters; and diagnosing the mechanical structural parts by successively calculating the progress of corrosion damage based on the corrosion damage resistance properties, with a period of time limited to that during which the corrosive environment inflicts corrosive damage on the mechanical structural parts materials, whereby quantitatively treats corrosive environment damage diagnosis of the mechanical structural parts (see e.g. JP 2001-41860 A).
Further, there has been proposed a water quality monitor for vapor condensed water and an energy conversion system used thereof, comprising producing condensed water by a condensing chamber provided for simulation of condensation conditions in the vicinity of a surface of a steam turbine blade; monitoring water quality by analyzing the condensed water; and measuring pH, electric conductivity, ingredient and concentration of chemical species, corrosion potential, and the total organic carbon concentration; and performing control operating conditions of the steam turbine and injection of chemicals based on the measured results (e.g. see JP 09-170704 A).
Furthermore, there has been proposed a steam turbine system equipped with a condensed water storage to temporarily store condensed water discharged from a low-pressure turbine, for the purpose of previously and effectively preventing corrosion damage to turbine structural materials by injecting anti-corrosive chemicals as much as a proper quantity fit for corrosion patterns, wherein the system is arranged to immerse a sample electrode made of materials with the same ingredients as constructional materials of the low-pressure turbine and a reference electrode serving as a reference of potential into the condensed water in the condensed water storage; measure a potential difference between the reference electrode and the sample electrode by a chemical injection control device; and calculate types and injection volume of injection chemicals so that the measured potential difference falls within a potential range set by measuring pH of the condensed water and chloride ion concentration of the structural materials of the low-pressure turbine (e.g. see JP 08-74075 A).